Agricultural sprayers use nozzles for spraying a liquid which may be a fertilizer, a pesticide, a fungicide, or an insecticide, for example, onto agricultural crops. Traditional nozzles consist of an orifice with geometry controlling the flow rate, droplet size and spray pattern to the target. The flow rate through the orifice is mainly a function of the orifice area and geometry as well as the fluid pressure at the orifice (i.e., pressure just prior to the orifice). Since the orifice size is fixed, i.e., the orifice geometry doesn't change, the most common way to influence the flow rate through the nozzle is by changing pressure.
Changing the fluid pressure at the nozzle to influence flow rate changes has become common place on sprayers in order to allow for variable vehicle speed. Systems change the flow rate proportional to the vehicle speed in order to keep the application rate the same.
However, using the traditional fixed orifice nozzle has some limitations. The pressure versus flow relationship is a squared function. To double the flow requires increasing the pressure by a factor of four times. Unfortunately, changing pressure also changes atomization dynamics resulting in an impact on spray quality. Spray quality characteristics, namely, droplet size and the spray angle, both become smaller as pressure increases. These changes can negatively impact to spray deposit and spray drift. So, the need for a variable rate nozzle with uniform pressure has emerged.
U.S. Pat. No. 7,124,964 discloses a nozzle arrangement including a flexible spray tip which may be manipulated by a driven metering member which acts to selectively change the spray tip configuration in response to changes in vehicle speed so as to change the spray tip spray rate for maintaining a desired application rate. This nozzle arrangement has the disadvantage of requiring a specialized nozzle construction instead of less costly standard nozzle configurations.